A. Field of the Invention
This invention relates to magnetic recording media and a method of manufacturing the same, and more specifically relates to perpendicular magnetic recording media and a method of manufacturing the same. This perpendicular magnetic recording media is suitable as discrete-track media, or as patterned media, having satisfactory electromagnetic transducing characteristics and resulting in excellent productivity.
B. Description of the Related Art
Magnetic recording devices have been one type of information recording device providing support for our advanced information-based society in recent years, and as the volume of information handled as grown, there have been demands for higher recording densities in the magnetic recording media used in magnetic recording devices. In order to achieve high recording densities, the units in which magnetization inversions occur must be decreased. To this end, in addition to reducing the size of magnetic particles, it is important that the units of magnetization inversion be clearly separated and partitioned, in order to reduce the magnetic interaction between adjacent recording units.
Perpendicular magnetic recording may be used as a technology to achieve high recording densities, in place of longitudinal magnetic recording. At present, as the material for magnetic recording layers primarily used in perpendicular magnetic recording media, CoCr alloy crystalline films having a hexagonal close-packed (hcp) structure are being studied. The crystal orientation is controlled such that the c-axis is perpendicular to the film of the plane (that is, such that the c plane is parallel to the film plane) to perform perpendicular magnetic recording.
In order to accommodate still higher densities in magnetic recording media, efforts are being made to reduce the sizes of crystal grains forming the CoCr alloy crystalline film, to reduce the grain diameter distribution, and to decrease the magnetic interaction between grains, among other efforts.
A method employing a magnetic layer, generally called a granular magnetic layer, having a structure in which nonmagnetic nonmetal material, such as oxides and nitrides, surrounds the periphery of magnetic crystal grains, is used as one method to control the magnetic structure so as to enable higher densities. In a granular magnetic film, the nonmagnetic nonmetal grain boundary phase physically separates magnetic grains, so that the magnetic interaction between magnetic grains is reduced, and the formation of zigzag domain walls arising in recorded bit transition areas is suppressed, so that low-noise characteristics are obtained.
As the recording layer of perpendicular magnetic recording media, use of a granular magnetic layer has been proposed. For example, in IEEE Trans. Mag., Vol. 36, 2393 (2000), a perpendicular magnetic recording media is described which employs Ru as an underlayer, and CoPtCrO alloy having a granular structure as a magnetic layer. It is stated that as the film thickness of the Ru layer, which is the underlayer below the granular magnetic layer, is increased, the c-axis orientation is improved, and excellent magnetic characteristics and electromagnetic transducing characteristics are obtained as a result.
Further, it has been reported that, by using a CoNiPt target with SiO2 or another oxide added in RF sputtering film deposition, a granular recording film can be formed having a structure in which each magnetic crystal grain is surrounded by nonmagnetic oxides and is individually separated, so that reduced noise can be achieved (see U.S. Pat. No. 5,679,473). In such a granular magnetic film, the nonmagnetic nonmetal grain boundary phase physically separates magnetic particles, so that the magnetic interaction between magnetic particles is reduced. It is thought that by thus suppressing the formation of zigzag domains occurring in recorded bit transition regions, low-noise characteristics can be obtained.
Further, if a crystal orientation controlling layer is provided which has, as the crystal structure, the same hcp structure as the ferromagnetic crystal grains of the magnetic layer, then the Co grains in a magnetic layer formed thereupon will grow corresponding to the crystal properties (crystal grains) of the crystal orientation controlling layer, and oxides will be segregated and grow in the magnetic layer corresponding to the grain boundary porous areas or amorphous areas of the crystal orientation control layer. In other words, it is proposed that magnetic crystal grains be grown epitaxially on the crystal grains of the crystal orientation controlling layer. As a result, by causing the crystal orientation of the crystal orientation controlling layer to be carried over to the magnetic layer and controlling the crystal orientation of the magnetic layer, and moreover by causing amorphous-phase crystal grain boundaries to be formed, intervening on the periphery of crystal grains forming the magnetic layer, the crystal state of a granular-structure magnetic layer can be controlled (see Japanese Patent Laid-open No. 2003-123239 and Japanese Patent Laid-open No. 2003-242623).
Comparatively satisfactory magnetic characteristics and electromagnetic transducing characteristics are obtained from such granular perpendicular magnetic recording media. However, the granular perpendicular magnetic recording media of the past have been so-called “full-coverage films,” which are continuous films as shown in FIG. 1. In order to further raise recording densities, there is a need to prevent write blurring into adjacent tracks, reduce formation of zigzag domain walls due to randomly positioned grains, and reduce to the extent possible both the effects of thermal fluctuation as crystal grain sizes are decreased and magnetic interactions between magnetic grains.
Here what is proposed is discrete-track media. To clearly partition magnetization inversion units, here a magnetic line is created which completely cuts off magnetically the intervals between tracks, to artificially obtain boundaries between adjacent tracks. The abovementioned write blurring into adjacent tracks and formation of zigzag domain walls can be eliminated.
In addition, patterned media are attracting attention. Patterned media are the ultimate recoding media, in which islands separated into single magnetic domains, with shape and size artificially adjusted, are arranged in eye shapes, and recording is performed with one such island as one bit.
Various methods have been proposed for such discrete-track media and patterned media. For example, as indicated in FIG. 1 of Japanese Patent Laid-open No. 4-310621, in magnetic recording media having a high-permeability layer and magnetic layer on a substrate, by providing a high-permeability layer and a magnetic layer absence portion between track portions in which recording and reproduction are performed, media is proposed in which intermixing of recordings between tracks during reproduction can be reliably avoided.
Also, as seen in FIG. 1 of Japanese Patent Laid-open No. 56-119934, a method has been proposed for fabricating a magnetic sequence by forming a spiral-shape depressed portion by etching the surface of the disc-shaped substrate prior to media formation, and then embedding the media in the depressed portion.
Further, as seen in FIG. 1 of Japanese Patent No. 2513746, a method has been proposed for fabricating a magnetically isolated magnetic sequence by removing a portion of a soft magnetic layer and instead embedding a nonmagnetic guard band, and forming the magnetic recording layer thereupon.
Further, as seen in FIG. 2 of Japanese Patent Laid-open No. 2003-16622, a method has been proposed for fabricating a magnetic sequence in magnetic recording media comprising, on a nonmagnetic substrate, a soft magnetic layer, a crystal orientation control layer, and a perpendicular magnetic recording layer. In this media a soft magnetic layer has an absence depressed portion, in the area crystal orientation control layer positioned between data tracks and data tracks in which recording and playback are performed, to cause exhibition of discrete action. By filling the depressed portion with nonmagnetic material, a nonmagnetic layer is formed, and the crystal orientation control layer is formed only on places in which the absence depressed portion does not exist in the soft magnetic backing layer, with the magnetic recording layer formed thereupon.
In Japanese Patent Laid-open No. 2006-12285, a magnetic recording media is disclosed which comprises a recording layer divided into numerous recording elements in a prescribed protrusion/depression pattern. There is a substrate, a soft magnetic layer formed on the substrate, and an intermediate layer intervening on the soft magnetic layer. By means of this proposal, crosstalk can be prevented during recording to and reproduction from adjacent tracks, and also worsening of the recording and reproduction characteristics can be prevented through provision of the protrusion/depression pattern.
As explained above, in the discrete-track media and patterned media proposed in the past, a layer which is intentionally removed includes the magnetic layer, substrate, or soft magnetic layer, or both the soft magnetic layer and the crystal orientation control layer.
However, when removing material in the magnetic layer as in Japanese Patent Laid-open No. 4-310621 and Japanese Patent Laid-open No. 2006-12285, the magnetic recording layer itself is directly etched, so that damage to the magnetic recording layer due to etching, as well as corrosion of the magnetic recording layer due to remnant components of the etching gas or etching liquid, cause degradation of magnetic characteristics.
Further, in methods in which a spiral-shaped groove is formed and the groove is filled with a magnetic material to fabricate a magnetic sequence as in Japanese Patent Laid-open No. 56-119934, it is difficult to form a magnetic recording layer only in a minute groove while achieving satisfactory crystal orientation and perpendicular anisotropy, so that satisfactory magnetic characteristics cannot be expected.
Also, flattening processes are provided in which, after removing material from the soft magnetic layer by etching in Japanese Patent No. 2513746, or after removing material from the soft magnetic layer and crystal orientation control layer as in Japanese Patent Laid-open No. 2003-16622, the depressed area is filled with nonmagnetic material, and CMP (chemical-mechanical polishing) or another means is used to flatten the surface. This is because when large irregularities are present in the surface, the magnetic head flying stability worsens. However, it is difficult to fill minute and deep gaps uniformly without leaving any air voids. Further, in the case of minute and deep gaps, irregularities grow larger according to initial irregularities in the surface after filling. Hence, even in cases in which CMP of the surface is performed for flattening, the polishing amount becomes considerable, and film thickness control is not possible.
This invention was devised in consideration of such problems, and has as an object the provision of magnetic recording media in which degradation of magnetic characteristics at the time of fabrication, such as is seen in the discrete-track media and patterned media proposed in the past, does not occur, and which can be manufactured by a simple method and results in has excellent productivity. Thus, the present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.